There is a coup and the new regime (I'm pretty sure it was a military regime actually) declares themselves the Third Reich and decides to go looking for lebensraum in eastern Europe.
went and looked at the last chapter again.... it was sort of a coup, in that army reservists joined with the civilians in attacking the chancellor building, although it didn't seem to be a full out military coup (apparently, the military leadership suffered right alongside the civilian ones). The new government is a civilian one. The new (temporary) PM of sorts is a civilian, and there is a note that a new constitution is being drawn up, and the monarchy is out. While they don't out and out title their new regime the Third Reich, they say that they are building a Third Reich, so sorta. The new PM of sorts does say that he wants to absorb parts of AH and Denmark and other places.
Arming the US army (when the US by this point was an unstoppable industrial juggernaut that could easily supply itself and then some) and offering a "safe haven" from a mad-dog country that's rabidly attacking a white industrial power for ridiculously flimsy reason is also effectively fuck all, because the former is unnecessary beyond the first month and the latter isn't actually any help at all against a rabid enemy that will stop at nothing to attack America because of inherent German warmongering nature (or something like that).
the book does mention that the US eventually retools it's industry to make it's own rifles (primarily by copying the German field arm, ironically)... but those first couple of months when the US desperately needed to build up it's forces PDQ, the US industry was inadequate to do so, so the British arms were vital (rather like the north in the ACW).